In a known rotor assembly of a gas turbine engine, an annular array of blades is radially retained, via cooperating dovetail or fir-tree features, to a rotor disc. It is desirable to provide an annular seal plate to at least the downstream face of the rotor to axially retain the blades. The seal plate also provides a seal to prevent or limit undesirable gas leakage passing therethrough. U.S. Pat. No. 4,019,833 discloses such a retaining plate and rotor disc, each comprising a cooperating annular array of interlocking bayonet features that hold the retaining ring to the rotor disc. The blades engage with the plate to prevent its rotation with respect to the disc and consequent undesirable disconnection. However, it is preferable that the blades are not used for locking the plate as the blades are critical components and any damage caused could compromise their integrity and that of the engine. Furthermore, this prior art arrangement necessitates the fitting of a front retaining plate last and such fitting is difficult and time consuming.
U.S. Pat. No. 5,622,475 recites the use of a split-locking ring to secure an annular retaining plate. However, the split-locking ring, which contacts the disc and the retaining plate, is prone to movement during engine operation and causes fretting against the contact surfaces thus reducing the life of the parts. In certain circumstance, this fretting could initiate undesirable cracking. This arrangement is further disadvantaged in that a full annular locking ring incurs a significant weight penalty, particularly considering it is part of a high-speed rotating assembly.
The Trent 500 aero-engine of Rolls-Royce plc, which entered into service August 2002, comprised a bayoneted retaining ring and a number of locking plugs as shown in FIG. 2. The locking plugs are inserted between castellations on the disc and a retaining plate to prevent relative rotation therebetween. A wire is used to secure the locking plugs in place. However, in service it has been found that the wire is prone to failure partly due to high centrifugal forces and high temperatures.